An independent research group suggests sampling water in 720 West Virginia homes for a chemical that spilled into the water supply in January.

Researchers from the West Virginia Testing Assessment Project, or WV TAP, say that number of homes would be "statistically defensible" in determining whether affected households are chemical-free.

The group sampled 10 homes in February for crude MCHM using state taxpayer dollars. Each contained chemical traces, but the concentrations were about 675 times weaker than what federal officials call safe to drink. The report says levels of the chemical have continued to decline since the spill.

However, researchers say at the time of the writing of the 24-page report, some residents in the area continue to report odors in their tap water not detected before the spill.

It's unclear how much additional testing would cost. The group used $765,000 from the state to test 10 homes, along with conducting other related studies.